A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure, or the reverse, from a rotating to a stationary structure. Slip rings are used in a wide variety of electromechanical systems such as rotating robotic arms, rotating satellite dishes, and in a wide variety of electronic motors having rotating parts, stationary parts, and the requirement to transfer electrical current between those parts. Current slip ring designs allow for transfer of electrical current or electrical signals by various means, but require no external pressure form large weights on the rotating or stationary parts of the slip ring while performing the slip ring electrical transfer.
There are a wide variety of slip ring configurations, ranging from tubular shapes of varying lengths to flat disk shapes of varying diameters. But whatever the design current slip ring designs do not allow significant pressure form external weights on either the stationary or rotating portions of the slip ring. This external weight restriction is crucial in current slip ring designs. If significant weight pressure is applied to the slip ring while it's operating the slip ring will fail to operate. No current slip ring design has sufficiently addressed the problem of external weight pressure on the slip ring.
Additionally, current slip ring designs have maintenance issues because of the slip ring design. Some slip rings use electrically conductive brushes on an electrically conductive surfaces, as seen in U.S. Pat. No. 4,992,691 A (Mlynarz), but friction between these two parts eventually causes deterioration of the brushes or on the electrically conductive, rotating surfaces.
U.S. Pat. No. 5,923,114 A (Senni) uses electrically conductive spherical balls and cylindrical rods (or pins). Senni's use of pins provides a line contact between the static and rotating components instead of the multiple point contacts in the brush type slip rings. However, Senni's design restricts significant weight on either the stationary or rotating parts.
Other attempted solutions have tried a tubular style of slip ring, but this has not sufficiently addressed the significant weight pressure on a slip ring. The tubular style of slip ring reveals another design problem in prior art slip ring designs, the length of the stator tube. As the quantity of wires, electrical current, and electrical signal requirements increase, the length and width of the slip ring must increase in order to compensate for these added requirements. For example, U.S. Pat. No. 3,042,998 A (Parsley, Herbert, Henry, Smith) discloses a slip ring dealing with increased wires, electrical current, and electrical signal requirements and a flat disk slip ring compensates for the increased electrical requirements by increasing the diameter and thickness of the slip ring unit. But the design still restricts significant weight on either the stationary or rotating parts.
An example of a flat slip ring or pancake design is disclosed in U.S. Pat. No. 6,984,915 B2 (Galyean) and by U.S. Pat. No. 5,901,429 (Crockett). Each demonstrates the use of a plurality of concentric annular rings made of conductive material. In all these designs the number of wires and power draw will increase the size of the slip ring, and the size of the slip ring drives important overall design considerations in the overall end product. Design considerations such as how and where a larger slip ring will fit in the end product.
For example, the size of the slip ring is a key consideration in the development of a robotic arm base. The robotic designer has to consider the size and location of the slip ring while designing the robotic arm. The demands for higher power or more wires feeding into the slip ring increases the length or width of the tubular style slip ring, or the diameter or thickness of a pancake style slip ring, and as the length of the slip ring increases, the height of the robotic arm base must also increase. As the height increases, the production unit's center of gravity rises and the base must grow broader or heavier as a counterbalance.
The use of pancake style slip rings allows the robotic arm base to remain lower but increases the width of the slip ring to produce a stable overall unit. Thus, a key drawback of the pancake style slip ring in robotic arms or other slip ring locations is the amount of clear surface area required for the slip ring to operate.
An additional problem with current slip ring designs is the amount of surrounding equipment one has to remove to access the slip ring for maintenance or replacement.
Thus, a slip ring design is needed that will (a) allow significant external weight pressure on either the stationary or rotating sides of the slip ring, (b) improve the mechanical performance of the slip ring by simplifying the slip ring operation, (c) eliminate damage-prone wires from dangling on movable joints; and (e) allow simplified access the slip ring for maintenance or replacement of the slip ring. Additionally, these design improvements would dramatically reduce both production and maintenance costs.